Hard coating and hard-coating-covered member

ABSTRACT

A hard coating includes three kinds of alternately laminated layers. The three kinds of layers consist of two kinds of single composition layers and a nanolayer-alternated layer. The two kinds of single composition layers are constituted by respective two of an A composition, a B composition and a C composition, wherein the A composition is a nitride of AlCrα, the B composition is a nitride of AlCrSiβ, and the C composition is a nitride of AlCr(SiC)γ. The nanolayer-alternated layer includes two kinds of nanolayers which are constituted by respective two of the A composition, the B composition and the C composition and which are alternately laminated. Each of the two kinds of single composition layers has a thickness of 0.5-1000 nm. Each of the two kinds of nanolayers has a thickness of 0.5-500 nm, and the nanolayer-alternated layer has a thickness of 1-1000 nm.

TECHNICAL FIELD

The present invention relates to a hard coating and ahard-coating-covered member, and more particularly to such a hardcoating having excellent wear resistance and excellent weldingresistance.

BACKGROUND ART

A hard coating is provided to cover a surface of a substrate made ofcemented carbide, high-speed tool steel or the like, in various memberssuch as various machining tools and friction parts that are required tohave wear resistance, wherein the various machining tools includecutting tools such as an endmill, a milling cutter, a drill, a lathecutter and a cutting tip, and non-cutting tools such as a forming tapand a rolling tool. For example, in Patent Document 1, there is proposeda hard coating of a multilayer structure of AlCrN system/AlTiSiN system.In Patent Document 2, there is proposed a hard coating of a multilayerstructure of AlCrN system/CrN system. In Patent Document 3, there isproposed a hard coating of a multilayer structure of AlCr system/TiSisystem.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1]

Japanese Unexamined Patent Application Publication No. 2012-35378

[Patent Document 2]

Japanese Unexamined Patent Application Publication No. 2014-79834

[Patent Document 3]

Japanese Unexamined Patent Application Republication No. 2008-534297

DISCLOSURE OF THE INVENTION Object to be Achieved by the Invention

However, there is a possibility that the conventional hard coating alsocan not necessarily provide sufficiently satisfactory wear resistanceand welding resistance, for example, depending on machining conditionsand use conditions such as kinds of workpiece materials and cuttingspeeds, so that there is still a room for the improvement. For example,there is a case in which the wear resistance cannot be obtainedsufficiently when the cutting tool covered by the hard coating of themultilayer structure of AlCrN system/CrN system is used for cuttingoperations for cutting carbon steel, cast iron or the like.

The present invention was made in view of the background discussedabove. It is therefore an object of the present invention to provide ahard coating and a hard-coating-covered tool having a novel constructionthat is excellent in wear resistance and welding resistance.

Measures for Achieving the Object

Various experiments and studies made by the inventors of the presentinvention and their collaborators under the above-described situationrevealed a fact that excellent wear resistance and excellent weldingresistance can be obtained by using an A composition, a B compositionand a C composition and laminating them, for example, with certainthicknesses, wherein the A composition is a nitride of AlCrα wherein anoptional additive component α is at least one kind of element selectedfrom B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W, the B composition is anitride of AlCrSiβ wherein an optional additive component β is at leastone kind of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta andW, and the C composition is a nitride of Al Cr (SiC) γ wherein anoptional additive component γ is at least one kind of element selectedfrom B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W. The present invention wasmade based on the revealed fact.

A first invention is, in a hard coating that is to be adhered to asurface of a substrate so as to cover the surface of the substrate,characterized in that: (a) the hard coating has a total thickness of arange of 0.5-20 μm and includes three kinds of layers that arealternately laminated, wherein the three kinds of layers consist of twokinds of single composition layers and a nanolayer-alternated layer,wherein the two kinds of single composition layers are constituted byrespective two of an A composition, a B composition and a C composition,and wherein the nanolayer-alternated layer includes two kinds ofnanolayers which are constituted by respective two of the A composition,the B composition and the C composition and which are alternatelylaminated; (b) the A composition is a nitride that is represented by acomposition formula of Al_(a)Cr_(b)α_(c), wherein atomic ratios a, b, csatisfy 0.30≤a≤0.85, 0.15≤b≤0.70, 0≤c≤0.10 and a+b+c=1, and wherein anoptional additive component α is at least one kind of element selectedfrom B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; (c) the B composition isa nitride that is represented by a composition formula ofAl_(d)Cr_(e)Si_(f)β_(g), wherein atomic ratios d, e, f, g satisfy0.20≤d≤0.85, 0.10≤e≤0.50, 0.03≤f≤0.45, 0≤g≤0.10 and d+e+f+g=1, andwherein an optional additive component β is at least one kind of elementselected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; (d) the Ccomposition is a nitride that is represented by a composition formula ofAl_(h)Cr_(i) (SiC)_(jγk), wherein atomic ratios h, i, j, k satisfy0.20≤h≤0.85, 0.10≤i≤0.50, 0.03≤j≤0.45, 0≤k≤0.10 and h+i+j+k=1, andwherein an optional additive component γ is at least one kind of elementselected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W; (e) each of thetwo kinds of single composition layers has a thickness of a range of0.5-1000 nm; and (f) each of the two kinds of nanolayers has a thicknessof a range of 0.5-500 nm, and the nanolayer-alternated layer has athickness of a range of 1-1000 nm.

It is noted that the (SiC) of the C composition means that the (SiC) ispresent in the form of silicon carbide as a compound. Further, it isdifficult to accurately control the thickness of each layer throughoutthe whole area. Each of the thicknesses described in the presentdescription is an average thickness value, and the thickness may bepartially deviated from a corresponding one of the above-described valueranges as long as the average thickness value falls within thecorresponding one of the above-described value ranges.

A second invention is, in the hard coating of the first invention,characterized in that a ratio T1/T3 of the thickness T1 of one of thetwo kinds of the single composition layers to the thickness T3 of thenanolayer-alternated layer and a ratio T2/T3 of the thickness T2 of theother of the two kinds of the single composition layers to the thicknessT3 of the nanolayer-alternated layer are both in range of 0.2-10.

A third invention is, in the hard coating of the first or secondinvention, characterized in that a lowermost layer of the two kinds ofthe single composition layers and the nanolayer-alternated layer, whichare alternately laminated, is to be disposed directly on a surface ofthe substrate.

A fourth invention is, in the hard coating of the first or secondinvention, characterized in that: (a) the hard coating includes aninterface layer that is to be disposed between the hard coating and thesubstrate; (b), (c) the interface layer has a thickness of a range of10-1000 nm, and is provided by one of three kinds of layers that are:(b-1) a single composition layer constituted by one of the Acomposition, the B composition and the C composition; (b-2) ananolayer-alternated layer includes two kinds of nanolayers which areconstituted by respective two of the A composition, the B compositionand the C composition and which are alternately laminated, such thateach of the two kinds of nanolayers has a thickness of a range of0.5-500 nm; and (b-3) a layer of metal nitride, metal carbonitride ormetal carbide, which is constituted by at least one kind of elementselected from B, Al, Ti, Y, Zr, Hf, V, Nb, Ta, Cr and W.

A fifth invention is, in the hard coating of any one of the firstthrough fourth inventions, is characterized in that: (a) the hardcoating includes a surface layer providing an outermost surface of thehard coating; (b) the surface layer is provided by a single compositionlayer constituted by one of the A composition, the B composition and theC composition, or a nanolayer-alternated layer including two kinds ofnanolayers which are constituted by respective two of the A composition,the B composition and the C composition and which are alternatelylaminated such that each of the two kinds of nanolayers has a thicknessof a range of 0.5-500 nm; and (c) the surface layer has a thickness of arange of 5-1000 nm.

A sixth invention is a hard-coating-covered member including a substratewhose surface is partially or entirely covered with a hard coating, andthe hard-coating-covered member being characterized in that the hardcoating is the hard coating of any one of the first through fifthinventions.

A seventh invention is, in the hard-coating-covered member of the sixthinvention, is characterized in that the hard-coating-covered member isan intermittent cutting tool which includes cutting edges and which isto be rotated about an axis so as to perform an intermittent cuttingoperation by the cutting edges.

It is noted that, as long as a rounded value of an actual value iswithin a corresponding one of numerical ranges defined in theabove-described inventions, such an actual value is interpreted to bewithin the corresponding one of the numerical ranges.

Effects of the Invention

In the hard coating of the present invention described above, the singlecomposition layer constituted by the A composition has high hardness andis excellent in wear resistance, and the single composition layerconstituted by the B composition has high hardness and is excellent inwear resistance and oxidation resistance. Further, the singlecomposition layer constituted by the C composition has low bondabilitywith oxygen because Si is present in the form of SiC (silicon carbide)as a compound in the C composition, and the degree of hardness is highwith reduction of mechanical strength being low even at a temperature of1000° C. or higher because the SiC is a covalent bond, so that thesingle composition layer constituted by the C composition is excellentin heat resistance, wear resistance and oxidation resistance. Further,the components α, β, γ are added optionally added to the respective Acomposition, B composition and C composition, at a ratio of 10 at %(atomic %) or less, whereby it is possible to micronize crystalparticles of the coating and to control sizes of the particles of thecoating by controlling the addition amount, thereby enabling thehardness, toughness and lubricity of the coating to be adjusted. Owingto the construction in which the two kinds of single composition layersand the nanolayer-alternated layer having the above-describedcharacteristics are alternately laminated with predeterminedthicknesses, it has become possible to obtain the hard coating that isexcellent in the wear resistance, toughness, lubricity and weldingresistance. Owing to these features, in a case of a cutting tool, forexample, it has become possible to increase a service life of the toolin a cutting operation with various workpiece materials such as carbonsteel, cast iron, alloy steel and stainless steel, or in a severemachining condition such as high speed machining and dry machining.

In the second invention, since the ratio T1/T2 of the thickness T1 ofone of the two kinds of the single composition layers to the thicknessT3 of the nanolayer-alternated layer and the ratio T2/T3 of thethickness T2 of the other of the two kinds of the single compositionlayers to the thickness T3 of the nanolayer-alternated layer are both inrange of 0.2-10, the two kinds of single composition layers and thenanolayer-alternated layer are provided with appropriate thicknessesproviding certain characteristics, which make it possible toappropriately obtain performances such as the wear resistance andwelding resistance.

In the third invention, the lowermost layer of the three kinds of layersconsisting of the two kinds of the single composition layers and thenanolayer-alternated layer, which are alternately laminated, is to bedisposed directly on a surface of the substrate, so that a coatingformation cost can be made lower than in an arrangement in which theinterface layer or the like is provided in a boundary adjacent to thesubstrate.

In the fourth invention, the interface constituted by the predeterminedcomposition or compositions and having the predetermined thickness isprovided in the boundary adjacent to the substrate, so that it ispossible to increase an adhesion strength of the heard coating to thesubstrate.

In the fifth invention, the surface layer constituted by thepredetermined composition or compositions and having the predeterminedthickness is provided as an outermost layer of the hard coating, so thatit is possible to further improve certain coating performances such asthe wear resistance and welding resistance, by appropriately determiningthe composition or compositions and the thickness of the surface layerof the surface layer.

In the sixth invention relating to a hard-coating-covered member, withthe hard coating of each of the first through fifth inventions beingprovided, it is possible to obtain substantially the same effects as acorresponding one of the inventions.

In the seventh invention, the hard-coating-covered member is theintermittent cutting tool such as endmill and milling cutter, so thatimpact load is repeatedly applied to the hard-coating-covered member andthe hard-coating-covered member is easily heated when a cuttingoperation is intermittently performed by the cutting edges. Therefore,the hard coating of the present invention, which is capable of obtaininghigh wear resistance, high toughness and high welding resistance, isadvantageously used for such an intermittent cutting tool.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view showing, by way of example, a ball endmill towhich the present invention is applied.

FIG. 2 is an enlarged bottom view as seen from a side of a distal end ofthe ball endmill of FIG. 1.

FIG. 3 is a schematic view for explaining a coating structure of a hardcoating that is provided on the ball endmill of FIG. 1.

FIG. 4 is a schematic view for explaining another example of the coatingstructure of the hard coating that is provided on the ball endmill ofFIG. 1.

FIG. 5 is a schematic view for explaining still another example of thecoating structure of the hard coating that is provided on the ballendmill of FIG. 1.

FIG. 6 is a schematic view for explaining still another example of thecoating structure of the hard coating that is provided on the ballendmill of FIG. 1.

FIG. 7 is a schematic view for explaining still another example of thecoating structure of the hard coating that is provided on the ballendmill of FIG. 1.

FIG. 8 is a schematic view for explaining still another example of thecoating structure of the hard coating that is provided on the ballendmill of FIG. 1.

FIG. 9 is a schematic view for explaining an arc ion plating apparatusas an example of a physical vapor deposition apparatus for forming thehard coating of each of FIGS. 3-8 on a tool substrate.

FIG. 10 is a view showing kinds of constituent elements and theircontent ratios in an A composition constituting the hard coating of eachof test samples 1-50 that were used in a cutting test.

FIG. 11 is a view showing kinds of constituent elements and theircontent ratios in a B composition constituting the hard coating of eachof the test samples 1-50.

FIG. 12 is a view showing kinds of constituent elements and theircontent ratios in a C composition constituting the hard coating of eachof the test samples 1-50.

FIG. 13 is a view showing the coating structure of the hard coating ofeach of the test samples 1-50.

FIG. 14 is a view showing a coating hardness of the hard coating of eachof the test samples 1-50, and also a wear width, a cutting distance andan evaluation result that were measured or obtained in the cutting test.

MODES FOR CARRYING OUT THE INVENTION

The present invention is advantageously is applied to a hard coatingwhich is to be disposed on a surface of any one of various machiningtools that include rotary cutting tools such as an endmill, a millingcutter, a tap and a drill, non-rotary cutting tools such as a lathecutter, non-cutting tools such as a forming tap, a rolling tool and apress die. However, the present invention is applicable also to a hardcoating serving as a surface protective coating of a bearing member, asemiconductor device or the like, namely, a hard coating which is to bedisposed on any one of members other than the machining tools, and whichare required to have wear resistance and oxidation resistance. Further,the present invention is applicable also to a cutting tip that is to beattached to any one of various machining tools so as to be used. As atool substrate of a hard-coating-covered tool, cemented carbide,high-speed tool steel, cermet, ceramics, polycrystalline diamond (PCD),monocrystalline diamond, polycrystalline CBN or monocrystalline CBN isadvantageously used, although the other tool material also can be used.As a method of forming the hard coating, a PVD method (physical vapordeposition method) such as an arc ion plating, sputtering and PLD (pulselaser deposition) is advantageously used.

The hard coating includes three kinds of layers that are alternatelylaminated, wherein the three kinds of layers consist of two kinds ofsingle composition layers and a nanolayer-alternated layer, wherein thetwo kinds of single composition layers are constituted by respective twoof an A composition, a B composition and a C composition, and whereinthe nanolayer-alternated layer includes two kinds of nanolayers whichare constituted by respective two of the A composition, the Bcomposition and the C composition and which are alternately laminated.Therefore, for example, where the two kinds of single composition layersare constituted by the A composition and the B composition,respectively, and the two kinds of nanolayers included in thenanolayer-alternated layer are constituted by the A composition and theB composition, respectively, the C composition is not needed. Thus, thehard coating can be constituted by only two out of the A composition,the B composition and the C composition. Further, the two kinds ofsingle composition layers and the nanolayer-alternated layer may belaminated in an order that is appropriately determined. It is preferablethat the three kinds of layers consisting of the two kinds of singlecomposition layers and the nanolayer-alternated layer are laminated inthe predetermined order for at least one cycle, and that the three kindsof layers are laminated for a completed cycle or cycles so that numbersof the respective three kinds of layers are equal to one another.However, the lamination of the three kinds of layers may be terminatedwithout an uppermost layer of the three kinds of layers completing acorresponding cycle, for example, such that the uppermost layer is thesame in kind as a lowermost layer of the three kinds of layers. The samedescription is applied also to the nanolayer-alternated layer includingthe two kinds of nanolayers that are alternately laminated. Where thehard coating includes an interface layer and/or a surface layer, thetotal thickness of the hard coating includes a thickness of theinterface layer and/or a thickness of the surface layer.

It is preferable that a ratio T1/T3 of the thickness T1 of one of thetwo kinds of the single composition layers to the thickness T3 of thenanolayer-alternated layer and a ratio T2/T3 of the thickness T2 of theother of the two kinds of the single composition layers to the thicknessT3 of the nanolayer-alternated layer are both in a range of 0.2-10.However, each of the thicknesses T1, T2, T3 may be set to a value bywhich the corresponding ratio is deviated from the correspondingnumerical range. The hard coating may include an interface layer, asneeded, which is to be provided between the hard coating and thesubstrate. It is preferable that the interface layer is constituted by asingle composition layer constituted by one of the A composition, the Bcomposition and the C composition, or a nanolayer-alternated layerincludes two kinds of nanolayers which are constituted by respective twoof the A composition, the B composition and the C composition and whichare alternately laminated. However, the interface layer may be a layerof metal nitride, metal carbonitride or metal carbide, which isconstituted by at least one kind of element selected from B, Al, Ti, Y,Zr, Hf, V, Nb, Ta, Cr and W, or a layer constituted by anothercomposition or compositions. The interface layer has a thickness that ispreferably in a range of 10-1000 nm. However, the thickness of theinterface layer may be outside the numerical range of 10-1000 nm.

The hard coating may include a surface layer, as needed. It ispreferable that the surface layer is constituted by a single compositionlayer constituted by one of the A composition, the B composition and theC composition, or a nanolayer-alternated layer including two kinds ofnanolayers which are constituted by respective two of the A composition,the B composition and the C composition and which are alternatelylaminated. However, the surface layer may be a layer constituted byanother composition or compositions. The surface layer has a thicknessthat is preferably in a range of 5-1000 nm. However, the thickness ofthe surface layer may be outside the numerical range of 5-1000 nm.

According to the findings made by the inventors of the present inventionand their collaborators, owing to the alternate lamination of the threekinds of layers consisting of the two kinds of single composition layersand the nanolayer-alternated layer, the hard coating of the presentinvention provides higher oxidation resistance, hardness, wearresistance and shear strength, than a multilayer coating of AlCrN base.Further, high hardness can be realized owing to impedance of latticedislocation, which is made by an interface between each adjacent two ofthe layers having various elastic properties (modulus of elasticity anddegree of hardness). The interface contributes to not only increase ofthe coating hardness but also improvement of toughness, owing to thefunction of impeding energy dissipation and crack extension. On theother hand, since the interface largely influences on characteristics ofthe multilayer coating, the provision of the nanolayer-alternated layerin which a cycle of lamination of the nanolayers is in a range ofnanometers makes it possible to obtain effects of improvements ofmechanical properties and tribology of the hard coating, byappropriately adjusting sizes of the crystal particles and coatingdensity by controlling the thickness of each of the nanolayers of thenanolayer-alternated layer.

Embodiment

Hereinafter, an embodiment of the present invention will be described indetails with reference to the drawings.

FIG. 1 is a front view showing a ball endmill 10 that is an example of ahard-coating-covered member to which the present invention is applied.FIG. 2 is an enlarged bottom view as seen from a side of a distal end ofthe ball endmill 10. The ball endmill 10 includes a tool substrate 12(see FIGS. 3-8) constituted by cemented carbide, and the tool substrate12 includes a shank portion 14 and a blade portion 16 that are integralwith each other. The blade portion 16 is provided with a pair of cuttingedges that are symmetrical with respect to an axis of the ball endmill10, wherein each of the cutting edges includes a peripheral cutting edge18 and a ball-end cutting edge 20. With the ball endmill 10 beingrotated about the axis, the ball endmill 10 performs an intermittentcutting operation by the peripheral cutting edge 18 and the ball-endcutting edge 20 of each cutting edge. The peripheral cutting edge 18 andthe ball-end cutting edge 20 are smoothly connected to each other so asto be contiguous to each other. On respective opposite sides of eachcutting edge including the peripheral cutting edge 18 and the ball-endcutting edge 20, a rake face 22 and a flank face (relief face) 24 aredefined. In other words, the peripheral cutting edge 18 and the ball-endcutting edge 20 are provided on a ridge line that is an intersection ofthe rake face 22 and the flank face 24. The ball endmill 10 is ahard-coating-covered tool, and corresponds to an intermittent cuttingtool.

A hard coating 30 shown in FIG. 3 is provided to cover a surface of theblade portion 16 that is a portion of the tool substrate 12. FIG. 3 is aschematic view showing in enlargement a cross section of a neighborhoodof the surface of blade portion 16 covered by the hard coating 30. Aregion of the surface covered by the hard coating 30 is represented by ahatched area in FIG. 1. It is also possible to provide the hard coating30 such that an entirety of the ball endmill 10 including also the shankportion 14 is covered with the hard coating 30.

The hard coating 30 has a multilayer structure, and includes an A layer32, a B layer 34 and a nanolayer-alternated layer 36 that are arrangedin this order of description as seen in a direction away from an outersurface of the hard coating 30 toward the tool substrate 12. The A layer32, the B layer 34 and the nanolayer-alternated layer 36 are laminatedfor at least one cycle. The hard coating 30 further includes aninterface layer 38 that is provided in its boundary portion adjacent tothe tool substrate 12. That is, the interface layer 38 is first disposedon a surface of the tool substrate 12, and then the nanolayer-alternatedlayer 36, B layer 34 and A layer 32 are disposed on the interface layer38. The nanolayer-alternated layer 36, B layer 34 and A layer 32 arelaminated repeatedly in this order of description, such that anuppermost portion of the hard coating 30 is provided by the A layer 32.The hard coating 30 including the interface layer 38 has a totalthickness Ttotal that is appropriately set to a value within a range of0.5-20 μm. The A layer 32 has a thickness T1 that is appropriately setto a value within a range of 0.5-1000 nm. The B layer 34 has a thicknessT2 that is appropriately set to a value within a range of 0.5-1000 nm.The nanolayer-alternated layer 36 has a thickness T3 that isappropriately set to a value within a range of 1-1000 nm. Further, thethicknesses T1-T3 are set to the respective values such that a ratioT1/T3 of the thickness T1 to the thickness T3 and a ratio T2/T3 of thethickness T2 to the thickness T3 are both in a range of 0.2-10.

The A layer 32 is a single composition layer that is constituted by onlyan

A composition. The A composition is a nitride represented by acomposition formula of Al_(a)Cr_(b)α_(c), wherein atomic ratios a, b, csatisfy 0.30≤a≤0.85, 0.15≤b≤0.70, 0≤c≤0.10 and a+b+c=1, and wherein anoptional additive component α is at least one kind of element selectedfrom B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W. FIG. 10 is a view showingexamples of a content (at %) of each element of the A composition,wherein each blank represents that the content (at %) of thecorresponding element is 0, and each gray part (column provided withscatter points) represents that the atomic ratio corresponding to thecontent of the corresponding element is deviated from the correspondingnumerical range of the above-described composition formula. That is, thetest samples 7-50 satisfy requirements of the A composition. The A layer32 having such a composition has features of high hardness and excellentwear resistance. Further, with addition of the optional additivecomponent α with the ratio not larger than 10 at %, it is possible tomicronize crystal particles and to control sizes of the particles bycontrolling the addition amount, whereby the hardness, toughness andlubricity of the coating can be adjusted.

The B layer 34 is a single composition layer that is constituted by onlya B composition. The B composition is a nitride represented by acomposition formula of Al_(d) Cr_(e)Si_(f)β_(g), wherein atomic ratiosd, e, f, g satisfy 0.20≤d≤0.85, 0.10≤e≤0.50, 0.03≤f≤0.45, 0≤g≤0.10 andd+e+f+g=1, and wherein an optional additive component β is at least onekind of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W.FIG. 11 is a view showing examples of a content (at %) of each elementof the B composition, wherein each blank represents that the content (at%) of the corresponding element is 0, and each gray part (columnprovided with scatter points) represents that the atomic ratiocorresponding to the content of the corresponding element is deviatedfrom the corresponding numerical range of the above-describedcomposition formula. That is, the test samples 7-50 satisfy requirementsof the B composition. The B layer 34 having such a composition hasfeatures of high hardness and excellent wear resistance and excellentoxidation resistance. As the above-described optional additive componentα, the optional additive component β is at least one kind of elementselected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W. With addition ofthe optional additive component β with the ratio not larger than 10 at%, it is possible to micronize crystal particles and to control sizes ofthe particles by controlling the addition amount, whereby the hardness,toughness and lubricity of the coating can be adjusted.

The nanolayer-alternated layer 36 has multilayer structure including anA nanolayer 32 n and a B nanolayer 34 n that are alternately laminatedfor at least one cycle, wherein the A nanolayer 32 n is constituted bythe A composition as the A layer 32, and the B nanolayer 34 n isconstituted by the B composition as the B layer 34. In this embodiment,a lowermost portion of the nanolayer-alternated layer 36, which isadjacent to the A layer 32, is provided by the A nanolayer 32 n, whilean uppermost portion of the nanolayer-alternated layer 36, which isadjacent to the B layer 34, is provided by the B nanolayer 34 n.However, the lowermost portion and the uppermost portion of thenanolayer-alternated layer 36 may be provided by the B nanolayer 34 nand the A nanolayer 32 n, respectively. The A nanolayer 32 n and the Bnanolayer 34 n have respective thicknesses each of which isappropriately set to a value within a range of 0.5-500 nm. Thenanolayer-alternated layer 36 has features of high hardness, excellentwear resistance, excellent toughness and excellent oxidation resistance.That is, the interface between the nanolayers 32 n, 34 n contributes toincrease of the coating hardness and also improvement of toughness owingto the function of impeding energy dissipation and crack extension.Further, since a cycle of lamination of the nanolayers 32 n, 34 n is ina range of nanometers, it is possible to obtain effects of improvementsof mechanical properties and tribology of the hard coating, byappropriately adjusting sizes of the crystal particles and coatingdensity by controlling the thickness of each of the nanolayers 32 n, 34n.

The interface layer 38 is a single composition layer constituted by onlythe A composition as the A layer 32. The interface layer 38 has athickness that is appropriately set to a value within a range of 10-1000nm. With the interface layer 38 being provided in a boundary adjacent tothe tool substrate 12, an adhesion strength of the hard coating 30 tothe tool substrate 12 can be increased.

FIGS. 4-8 are views for explaining other examples of the hard coatingseach of which is to be disposed on the surface of the blade portion 16of the ball endmill 10. Each of FIGS. 4-8 is a cross-sectional schematicview corresponding to the view of FIG. 3, and the total thickness Ttotalof any one of the hard coatings is in a range of 0.5-20 μm. A hardcoating 40 of FIG. 4 is opposite to the above-described hard coating 30in terms of order of laminations of the A layer 32 and the B layer 34.In the hard coating 40 of FIG. 4, the A layer 32 is disposed between theB layer 34 and the nanolayer-alternated layer 36, and the B layer 34provides the uppermost or outermost layer. Further, an interface layer42 of a C composition is provided in place of the interface layer 38 ofthe A composition. The C composition is a nitride that is represented bya composition formula of Al_(h)Cr_(i)(SiC)_(jγk), wherein atomic ratiosh, i, j, k satisfy 0.20≤h≤0.85, 0.10≤i≤0.50, 0.03≤j≤0.45, 0≤k≤0.10 andh+i+j+k=1, and wherein an optional additive component γ is at least onekind of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W.FIG. 12 is a view showing examples of a content (at %) of each elementof the C composition, wherein each blank represents that the content (at%) of the corresponding element is 0, and each gray part (columnprovided with scatter points) represents that the atomic ratiocorresponding to the content of the corresponding element is deviatedfrom the corresponding numerical range of the above-describedcomposition formula. That is, the test samples 7-50 satisfy requirementsof the C composition. The interface layer 42 is a single compositionlayer constituted by only the C composition, and has a thickness that isappropriately set to a value within a range of 10-1000 nm. With theinterface layer 42 being provided in a boundary adjacent to the toolsubstrate 12, an adhesion strength of the hard coating 40 to the toolsubstrate 12 can be increased.

In a hard coating 50 of FIG. 5, a C layer 52 constituted by only the Ccomposition is provided in place of the above-described B layer 34, anda nanolayer-alternated layer 54 is provided in place of theabove-described nanolayer-alternated layer 36. The nanolayer-alternatedlayer 54 includes an A nanolayer 32 n constituted by the A compositionand a C nanolayer 52 n constituted by the C composition, such that the Ananolayer 32 n and the C nanolayer 52 n are alternately laminated for atleast one cycle. Each of the C layer 52 and C nanolayer 52 n has lowbondability with oxygen because Si is present in the form of SiC(silicon carbide) as a compound in the C composition, and the degree ofhardness is high with reduction of mechanical strength being low even ata temperature of 1000° C. or higher because the SiC is a covalent bond,so that the C layer 52 and C nanolayer 52 n have features of excellentheat resistance, excellent wear resistance and excellent oxidationresistance. As the above-described optional additive component α, theoptional additive component γ is at least one kind of element selectedfrom B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W. With addition of theoptional additive component γ with the ratio not larger than 10 at %, itis possible to micronize crystal particles and to control sizes of theparticles by controlling the addition amount, whereby the hardness,toughness and lubricity of the coating can be adjusted. The C layer 52is a single composition layer constituted by only the C composition. TheC layer 52 has a thickness which is appropriately set to a value withina range of 0.5-1000 nm such that a ratio of the thickness of the C layer52 to the thickness of the nanolayer-alternated layer 54 is in a rangeof 0.2-10. In this embodiment, a lowermost portion of thenanolayer-alternated layer 54, which is adjacent to the C layer 52, isprovided by the C nanolayer 52 n, while an uppermost portion of thenanolayer-alternated layer 54, which is adjacent to the A layer 32, isprovided by the A nanolayer 32 n. However, the lowermost portion and theuppermost portion of the nanolayer-alternated layer 54 may be providedby the A nanolayer 32 n and the C nanolayer 52 n, respectively. Thenanolayer-alternated layer 54 has a thickness that is appropriately setto a value within a range of 1-1000 nm. The A nanolayer 32 n and the Cnanolayer 52 n have respective thicknesses each of which isappropriately set to a value within a range of 0.5-500 nm. Asabove-described the nanolayer-alternated layer 36, thenanolayer-alternated layer 54 has features of high hardness, excellentwear resistance, excellent toughness and excellent oxidation resistance.Further, the hard coating 50 includes an interface layer 56 that is asingle composition layer constituted by only the above-described Bcomposition.

A hard coating 60 of FIG. 6 is different from the above-described hardcoating 30 of FIG. 3 in terms of order of laminations of the A layer 32,B layer 34 and nanolayer-alternated layer 36. In the hard coating 60 ofFIG. 6, the nanolayer-alternated layer 36, A layer 32 and B layer 34 arelaminated in this order of description as seen in a direction away fromthe outer surface of the hard coating 30 toward the tool substrate 12.Further, the hard coating 60 includes an interface layer 62 that isprovided between the lowermost B layer 34 and the tool substrate 12,wherein the interface layer 62 is a nanolayer-alternated layer includestwo kinds of the A nanolayer 32 n, B nanolayer 34 n and C nanolayer 52n, and wherein the two kinds of nanolayers are alternately laminated.The interface layer 62 has a thickness that is appropriately set to avalue within a range of 10-1000 nm, and each of the two kinds ofnanolayers has a thickness that is appropriately set to a value within arange of 0.5-500 nm.

A hard coating 70 of FIG. 7 is different from the above-described hardcoating 30 of FIG. 3 in that the interface layer 38 is absent.

A hard coating 80 of FIG. 8 is different from the above-described hardcoating 30 of FIG. 3 in that a surface layer 82 provides an outermostsurface of the hard coating 80 and in that an interface layer 84 isconstituted by a composition or compositions that are other the Acomposition, B composition and C composition. The surface layer 82 is,for example, a nanolayer-alternated layer including the A nanolayer 32 nand B nanolayer 34 n that are alternately laminated, as thenanolayer-alternated layer 36. The surface layer 82 has a thickness thatis appropriately set to a value within a range of 5-1000 nm, and each ofthe A nanolayer 32 n and B nanolayer 34 n has a thickness that isappropriately set to a value within a range of 0.5-500 nm. The interfacelayer 84 is constituted by metal nitride, metal carbonitride or metalcarbide, which is constituted by at least one kind of element selectedfrom B, Al, Ti, Y, Zr, Hf, V, Nb, Ta, Cr and W, and has a thickness thatis appropriately set to a value within a range of 10-1000 nm.

Further, the hard coating can be constituted in other forms, althoughnot being shown in drawings. For example, the nanolayer-alternated layer36 of the above-described hard coating 30 includes the A nanolayer 32 nand B nanolayer 34 n that are alternately laminated. However, thenanolayer-alternated layer 36 may be constructed to include the Cnanolayer 52 n. That is, where the single composition layers areconstituted by the A layer 32 and B layer 34, the nanolayer-alternatedlayer may be constituted by the nanolayer-alternated layer 36 includingthe A nanolayer 32 n and C nanolayer 52 n that are alternatelylaminated, or the nanolayer-alternated layer 36 including the Bnanolayer 34 n and C nanolayer 52 n that are alternately laminated.

Further, the single composition layers are constituted by the A layer 32and B layer 34 in the hard coating 30, and the single composition layersare constituted by the A layer 32 and C layer 52 in the hard coating 50.However, the two kinds of single composition layers may be constitutedby the B layer 34 and C layer 52.

Further, the surface layer 82 of the hard coating 80 is thenanolayer-alternated layer including the A nanolayer 32 n and Bnanolayer 34 n that are alternately laminated. However, the surfacelayer 82 may be a nanolayer-alternated layer including the C nanolayer52 n. Further, the surface layer 82 may be a single composition layerconstituted by the A composition, B composition or C composition.

Further, in each of the hard coatings 30, 40, 50, 60, 70, 80, the threekinds of layers, which consist of the two kinds of single compositionlayers (that are respective two of the A layer 32, B layer 34 and Clayer 52) and one of the nanolayer-alternated layers 36, 54, arealternately laminated in a predetermined order for a completed cycle orcycles so that numbers of the respective three kinds of layers are equalto one another. However, the lamination of the three kinds of layers maybe terminated without an uppermost or outermost layer of the three kindsof layers completing a corresponding cycle, for example, such that the Alayer 32, which provides the uppermost layer of the hard coating 30, isomitted. In other words, also in each of the hard coatings 30, 40, 50,60, 70 in which the surface layer is not provided, the outermost layermay be regarded as a surface layer other than the three kinds of layersthat are alternately laminated. Regarding each of thenanolayer-alternated layers 36, 54 including the two kinds of nanolayers(that are respective two of the A nanolayer 32 n, B nanolayer 34 n and Cnanolayer 52 n) alternately laminated, too, the number of laminatednanolayers may be an odd number, for example, such that thenanolayer-alternated layer 36 is initiated with the A nanolayer 32 n andis ended with the A nanolayer 32 n.

FIG. 13 is a view specifically showing a coating structure of the hardcoating of each of test samples 1-50 of endmills. In column of “SINGLECOMPOSITION LAYER”, “A LAYER”, “B LAYER” and “C LAYER” correspond to theabove-described A layer 32, B layer 34 and C layer 52, respectively.Further, in column of “NANOLAYER-ALTERNATED LAYER”, “A LAYER”, “B LAYER”and “C LAYER” correspond to the above-described A nanolayer 32 n, Bnanolayer 34 n and C nanolayer 52 n, respectively. “INTERFACE LAYER”corresponds to the above-described interface layers 38, 42, 56, 62, 84.Each blank in “A LAYER”, “B LAYER” and “C LAYER” in column of “SINGLECOMPOSITION LAYER”, “A LAYER”, “B LAYER” and “C LAYER” in column of“NANOLAYER-ALTERNATED LAYER”, and “INTERFACE LAYER” represents that thecorresponding layer is not provided. For example, in the test sample 27without the interface layer, the single composition layers are the Alayer and the C layer, and the nanolayer-alternated layer includes the Ananolayer and the C nanolayer that are alternately laminated, so thatcomponents of the B composition described in FIG. 11 are notsubstantially included in the test sample 27. Further, in the testsample 45 without the interface layer, the single composition layers arethe B layer and the C layer, and the nanolayer-alternated layer includesthe B nanolayer and the C nanolayer that are alternately laminated, sothat components of the A composition described in FIG. 10 are notsubstantially included in the test sample 45. In each of the other testsamples, either, all of components of the A composition, B compositionand C composition described in FIGS. 10-12 are not necessarily included,as long as the hard coating is constituted by at least two of the Acomposition, B composition and C composition. Further, none of the testsamples 1-50 shown in FIG. 13 is provided with the surface layer. InFIG. 13, each gray part (column provided with scatter points) representsthat a corresponding one of requirements regarding thicknesses of thepresent embodiment (claim 1 of the present invention) is not satisfied,and the test samples 1-6 are comparative products while the test samples7-50 are products of the present invention.

FIG. 9 is a schematic construction view (schematic view) for explainingan arc ion plating apparatus 100 used for forming the above-describedhard coatings 30, 40, 50, 60, 70, 80 or the hard coatings of the testsamples 1-50 described in FIG. 13 (hereinafter simply referred to “hardcoating 30 or the like” where they are not to be distinguished from oneanother), onto the tool substrate 12. The arc ion plating apparatus 100is configured to form the hard coating 30 or the like onto the surfaceof the tool substrate 12 through an arc ion plating as a kind of PVDmethod, and is capable of continuously forming a plurality of kinds oflayers that are different in composition, with predeterminedthicknesses, by switching an evaporation source (target) and a reactiongas. For example, when the hard coating 30 is to be formed, thenanolayer-alternated layer 36, B layer 34, and A layer 32 arealternately laminated after the interface layer 38 is formed on thesurface of the tool substrate 12. FIG. 9 corresponds to a plane view ofthe arc ion plating apparatus 100 as seen from an upper side of the arcion plating apparatus 100.

The arc ion plating apparatus 100 includes: a rotary table 154 to bedriven to be rotated about a rotation axis S extending substantially ina vertical direction and to hold a plurality of workpieces, i.e., theplurality of tool substrates 12 on each of which the hard coating 30 orthe like is to be formed; a bias-voltage power source 156 for applying anegative bias voltage to the tool substrates 12; a processing vessel inthe form of a chamber 158 which accommodates therein the tool substrates12; a reaction-gas supplying device 160 for supplying a reaction gasinto the chamber 158; a gas discharging device 162 for discharging a gasfrom an interior of the chamber 158 by, for example, a vacuum pump so asto reduce a pressure in the interior of the chamber 158; a first arcpower source 164; a second arc power source 166, a third arc powersource 168 and a fourth arc power source 170. The rotary table 154 is adisk-shaped table whose center corresponds to the above-describedrotation axis S. The plurality of tool substrates 12 are disposed in anouter peripheral portion of the rotary table 154 such that each of thetool substrates 12 has an attitude that causes each substrate 12 issubstantially parallel to the rotation S. While the tool substrates 12are rotated about the rotation axis S by the rotary table 154, each ofthe tool substrates 12 may be rotated about its axis. When the nitrideof the A layer 32, B layer 34, C layer 52 or the like is to be formed,the reaction-gas supplying device 160 supplies nitrogen gas into thechamber 158. An inside of the chamber 158 is placed in a vacuum state ofabout 2-10 Pa, for example, by the gas discharging device 162, and isheated by a heater or the like not shown in the drawings, to a vapordeposition temperature of about 300-600° C., for example.

Each of the first arc power source 164; second arc power source 166,third arc power source 168 and fourth arc power source 170 is configuredto selectively energize between a corresponding one of anodes 174, 178,182, 186 and a corresponding one of cathodes in the form of firstevaporation source 172, second evaporation source 176, third evaporationsource 180 and fourth evaporation source 184 that are made of vapordeposition material, with an arc current, so as to cause an arcdischarge, thereby selectively causing evaporation material to evaporatefrom the corresponding one of the first evaporation source 172, secondevaporation source 176, third evaporation source 180 and fourthevaporation source 184. After having being evaporated, the evaporationmaterial becomes positive ion that is deposited to cover each of thetool substrates 12 to which negative (−) bias voltage is applied. Thatis, each of the evaporation sources 172, 176, 180, 184 is constituted byan alloy of one of the A composition, B composition and C composition,so that one of the evaporation sources can serve as an extra source thatis constituted by, for example, the alloy of one of the A composition, Bcomposition and C composition, which is to be formed with a relativelylarge thickness, for thereby making it possible to efficiently performthe coating formation. The number of the evaporation sources may bethree so as to correspond to the number of the compositions constitutingthe hard coating 30 or the like. Further, in a case in which the hardcoating 30 or the like is constituted by only two of the A composition,B composition and C composition, the four evaporation sources 172, 176,180, 184 may be grouped into two groups such that two of the evaporationsources 172, 176, 180, 184 belonging to one of the two groups areconstituted by the alloy of one of the two of the A composition, Bcomposition and C composition while the other two of the evaporationsources 172, 176, 180, 184 belonging to the other of the two groups areconstituted by the alloy of the other of the two of the A composition, Bcomposition and C composition.

The above-described arc power sources 164, 166, 168, 170 are switched asneeded so as to sequentially form the layers of predeterminedcompositions, whereby the hard coating 30 or the like having apredetermined coating structure can be obtained. The thickness of eachlayer can be adjusted by controlling a rotational speed of the rotarytable 154 and a length of time of energization of a corresponding one orones of the arc power sources 164, 166, 168, 170. A boundary portionlocated between a plurality of layers that are different in compositionmay be provided with a mixture layer constituted by a mixture of twokinds of compositions.

There will be described a result of performance test of the hardcoatings, which was made by preparing the test samples 1-50 in which thehard coatings having the respective coating structures shown in FIGS.10-13 are disposed on a two-teeth ball endmill with the tool substrate12 made of cemented carbide and with a diameter of 6 mm (nose radius R=3mm), as in the above-described ball endmill 10. FIG. 14 is a viewshowing the test result, wherein “COATING HARDNESS” represents a HVvalue (Vickers hardness) of each hard coating that was measured under acondition indicated by hardness symbol HV0.025, in accordance withVickers hardness test method (JIS G0202, Z2244). Further, a cuttingoperation was made by using each of the test samples 1-50, in accordancewith a cutting test condition described below, and a cutting distanceand a wear width of the relief face (flank face) adjacent to theball-end cutting edge 20 were measured and a coating performance (wearresistance) was evaluated. The evaluation of the coating performance wasmade by suspending the cutting operation, basically, in an appropriatestage in which the cutting distance has reached 500 m or more, and thenmeasuring the cutting distance and the wear width of the relief face. Ina case in which the wear width of the relief face was enlarged (to 0.3mm or more), the cutting operation was suspended even with the cuttingdistance being not longer than 500 m, and the cutting distance and thewear width of the relief face were measured when the cutting operationwas suspended. The wear width of the relief face is a maximum widthvalue, and was measured by suspending the cutting operation each timethe cutting distance reached to a predetermined distance value, so thatthe wear width was measured visually by using a measuring microscope(MM-400/LM) manufactured by Nikon Corporation.

(Cutting Test Condition)

Workpiece material: S50C (mechanical structural carbon steel defined byJIS)Cutting velocity: 254 m/minNumber of revolutions: 13500 mm⁻¹Feed rate: f=0.12 mm/t, F=3240 mm/minCutting depth: ap (axial direction)=0.3 mm, ae (radial direction)=0.6 mm

As is apparent from FIG. 14, regarding the coating hardness (HV0.025) ofthe surface, any one of the test samples 7-50 as the products of thepresent invention exhibited a high hardness value that is 3000 orhigher, providing an expectation of excellent wear resistance.Meanwhile, the test samples 1-6 as the comparative products exhibitedabout 2000-2700 as the hardness value. Regarding the wear width of therelief face and the cutting distance, any one of the test samples 7-50as the products of the present invention was able to perform the cuttingoperation over 500 m or more before the wear width of the relief facereached 0.2 mm, and accordingly exhibited excellent wear resistance andexcellent welding resistance. Meanwhile, in any one of the test samples1-6 as the comparative products, the wear width of the relief faceexceeded 0.3 mm before the cutting operation over 500 m was completed.In the evaluation, “∘” was given to a case in which the cuttingoperation over 500 m or more was done before the wear width of therelief face reached 0.2 mm, while “x” was given to a case in which thewear width of the relief face exceeded 0.2 mm before the cuttingdistance reached 500 mm, namely, in which a sufficient tool life was notobtained. In any one of the test samples 7-50 as the products of thepresent invention, “∘” was given in the evaluation result and anexcellent tool life was obtained. In the wear width and the cuttingdistance, each gray part (column provided with scatter points)represents that the wear width of the relief face exceeded 0.2 mm beforethe cutting distance reached 500 mm.

As described above, in the hard coating 30 or the like of the ballendmill 10 according to the present embodiment, the two kinds of singlecomposition layers, which are constituted by respective two of the Acomposition, B composition and C composition (i.e., respective two ofthe A layer 32, B layer 34 and C layer 52), and the one kind ofnanolayer-alternated layer (nanolayer-alternated layer 36, 54 or thelike) including the two kinds of nanolayers, which are constituted byrespective two of the A composition, B composition and C composition(i.e., respective two of the A nanolayer 32 n, B nanolayer 34 n and Cnanolayer 52 n) and are alternately laminated, are alternately laminatedwith predetermined thicknesses, it becomes possible to obtain excellentwear resistance, excellent toughness, excellent lubricity and excellentwelding resistance. Owing to these features, it has become possible toincrease a service life of the tool in a cutting operation with variousworkpiece materials such as carbon steel, cast iron, alloy steel andstainless steel, or in a severe machining condition such as high speedmachining and dry machining.

Further, since the ratio T1/T2 of the thickness T1 of one of the twokinds of the single composition layers to the thickness T3 of thenanolayer-alternated layer and the ratio T2/T3 of the thickness T2 ofthe other of the two kinds of the single composition layers to thethickness T3 of the nanolayer-alternated layer are both in range of0.2-10, the two kinds of single composition layers and the one kind ofnanolayer-alternated layer are provided with appropriate thicknessesproviding certain characteristics, which make it possible toappropriately obtain performances such as the wear resistance andwelding resistance.

Further, each of the hard coating 70 of FIG. 7 and the test samples 27,45, which is not provided with the interface layer, can be formed at areduced coating formation cost, and the ball endmill 10 including thehard coating 70 or the like can be manufactured at a cheap cost. On theother hand, each of the hard coatings 30, 40, 50, 60, 80 and the testsamples 7-26, 28-44 and 46-50, which is provided with the interfacelayer 38 or like having the predetermined composition or compositionsand the predetermined thickness, it is possible to increase the adhesionstrength of the hard coating 30 or the like to the tool substrate 12.

Further, in the hard coating 80 of FIG. 8, which is provided with thesurface layer 82 having the predetermined composition or compositionsand the predetermined thickness, it is possible to further improvecertain coating performances such as the wear resistance and weldingresistance, by appropriately determining the composition or compositionsand the thickness of the surface layer 82.

Further, the ball endmill 10 is the intermittent cutting tool that is tointermittently perform a cutting operation by the peripheral cuttingedge 18 and the ball-end cutting edge 20, so that impact load isrepeatedly applied to the peripheral cutting edge 18 and ball-endcutting edge 20 and accordingly the peripheral cutting edge 18 andball-end cutting edge 20 are easily heated during the cutting operation.However, with provision of the hard coating 30 or the like having highwear resistance, high toughness and high welding resistance, it ispossible to increase the service life of the tool.

While the embodiment of the present invention has been described indetail by reference to the accompanying drawings, it is to be understoodthat the described embodiment is merely an embodied form and that thepresent invention can be embodied with various modifications andimprovements on the basis of knowledge of those skilled in the art.

DESCRIPTION OF REFERENCE SIGNS

10: ball endmill (hard-coating-covered member, intermittent cuttingtool), 12: tool substrate (substrate), 18: peripheral cutting edge(cutting edge), 20: ball-end cutting edge (cutting edge), 30, 40, 50,60, 70, 80: hard coating, 32: A layer (single composition layer), 32 n:A nanolayer (nanolayer), 34: B layer (single composition layer), 34 n: Bnanolayer (nanolayer), 36, 54: nanolayer-alternated layer, 38, 42, 56,62, 84: interface layer, 52: C layer (single composition layer), 52 n: Cnanolayer (nanolayer), 82: surface layer, Ttotal: total thickness, T1:thickness of A layer (thickness of single composition layer), T2:thickness of B layer (thickness of single composition layer), T3:thickness of nanolayer-alternated layer

1. A hard coating that is to be adhered to a surface of a substrate soas to cover the surface of the substrate, wherein the hard coating has atotal thickness of a range of 0.5-20 μm and includes three kinds oflayers that are alternately laminated, wherein the three kinds of layersconsist of two kinds of single composition layers and ananolayer-alternated layer, wherein the two kinds of single compositionlayers are constituted by respective two of an A composition, a Bcomposition and a C composition, and wherein the nanolayer-alternatedlayer includes two kinds of nanolayers which are constituted byrespective two of the A composition, the B composition and the Ccomposition and which are alternately laminated; the A composition is anitride that is represented by a composition formula ofAl_(a)Cr_(b)α_(c), wherein atomic ratios a, b, c satisfy 0.30≤a≤0.85,0.15≤b≤0.70, 0≤c≤0.10 and a+b+c=1, and wherein an optional additivecomponent α is at least one kind of element selected from B, C, Ti, V,Y, Zr, Nb, Mo, Hf, Ta and W; the B composition is a nitride that isrepresented by a composition formula of Al_(d)Cr_(e)Si_(f)β_(g), whereinatomic ratios d, e, f, g satisfy 0.20≤d≤0.85, 0.10≤e≤0.50, 0.03≤f≤0.45,0≤g≤0.10 and d+e+f+g=1, and wherein an optional additive component β isat least one kind of element selected from B, C, Ti, V, Y, Zr, Nb, Mo,Hf, Ta and W; the C composition is a nitride that is represented by acomposition formula of Al_(h)Cr_(i)(SiC)_(jγk), wherein atomic ratios h,i, j, k satisfy 0.20≤h≤0.85, 0.10≤i≤0.50, 0.03≤j≤0.45, 0≤k≤0.10 andh+i+j+k=1, and wherein an optional additive component γ is at least onekind of element selected from B, C, Ti, V, Y, Zr, Nb, Mo, Hf, Ta and W;each of the two kinds of single composition layers has a thickness of arange of 0.5-1000 nm; and each of the two kinds of nanolayers has athickness of a range of 0.5-500 nm, and the nanolayer-alternated layerhas a thickness of a range of 1-1000 nm.
 2. The hard coating accordingto claim 1, wherein a ratio of the thickness of one of the two kinds ofthe single composition layers to the thickness of thenanolayer-alternated layer and a ratio of the thickness of the other ofthe two kinds of the single composition layers to the thickness of thenanolayer-alternated layer are both in range of 0.2-10.
 3. The hardcoating according to claim 1 wherein a lowermost layer of the two kindsof the single composition layers and the nanolayer-alternated layer,which are alternately laminated, is to be disposed directly on a surfaceof the substrate.
 4. The hard coating according to claim 1: wherein thehard coating includes an interface layer that is to be adjacent to thesubstrate; the interface layer has a thickness of a range of 10-1000 nm,and is provided by one of three kinds of layers that are: a singlecomposition layer constituted by one of the A composition, the Bcomposition and the C composition; a nanolayer-alternated layer includestwo kinds of nanolayers which are constituted by respective two of the Acomposition, the B composition and the C composition and which arealternately laminated, such that each of the two kinds of nanolayers hasa thickness of a range of 0.5-500 nm; and a layer of metal nitride,metal carbonitride or metal carbide, which is constituted by at leastone kind of element selected from B, Al, Ti, Y, Zr, Hf, V, Nb, Ta, Crand W.
 5. The hard coating according to claim 1, wherein the hardcoating includes a surface layer providing an outermost surface of thehard coating; the surface layer is provided by a single compositionlayer constituted by one of the A composition, the B composition and theC composition, or a nanolayer-alternated layer including two kinds ofnanolayers which are constituted by respective two of the A composition,the B composition and the C composition and which are alternatelylaminated such that each of the two kinds of nanolayers has a thicknessof a range of 0.5-500 nm; and the surface layer has a thickness of arange of 5-1000 nm.
 6. A hard-coating-covered member including asubstrate whose surface is partially or entirely covered with, the hardcoating according to claim
 1. 7. The hard-coating-covered memberaccording to claim 6, wherein the hard-coating-covered member is anintermittent cutting tool which includes cutting edges and which is tobe rotated about an axis so as to perform an intermittent cuttingoperation by the cutting edges.